In typical oil and gas extraction techniques, tubing conveyed strings are often lowered into wells through a gate valve assembly that forms a part of subsea well control packages (WCP). In the context of subsea oil wells, a subsea WCP is installed to provide means to isolate and seal the well in emergencies. Such gate valve assemblies utilize gate valves to shut off or open a path through the gate valve assembly. Ideally, it is desirable that the tubing conveyed strings are removed from the gate assembly before the gate valve is completely closed. However, during emergencies, the time taken to perform the shutting down or sealing operation should be the minimized and a shearing of the tubing conveyed strings are preferred.
The gate valve assembly typically includes a valve body having a valve chamber therein with an inlet port and an outlet port (along a valve bore), and a linearly moveable gate having a through hole which when aligned with the inlet and outlet ports forms a path. The gate is moved linearly to open and close the flow path by means of actuating mechanisms. During operations which require the shutting down of an oil or gas well, there is a need for a mechanism that is capable of shearing the tubing conveyed strings.
To accomplish this, existing gate valves have been designed to have shearing surfaces on the inner circumferential edges of either the gate or seat flow passage so that when the gate is moved from an “open” position to a “closed” position, the tubing conveyed strings are sheared by the shearing surfaces. In typical cases of “double shear” gate valves, such shearing will cause tubing conveyed strings cutting (or slug pieces) to remain in the through hole of the cutting gate when the gate valve moves from the open position to the closed position. The tubing conveyed strings cuttings may obstruct or jam the gate valve when the gate valve moves back to the “open” position from the “closed” position. The tubing conveyed strings cuttings might fall into the valve bore (well) when the gate valve moves from the closed position to open position. Such a jamming or falling of the pieces into the well is undesirable in certain scenarios.
Existing cutting gate valves designed to address the aforementioned problems have included the use of a recessed cutting edge for wireline cutting operations. Such a recessed cutting edge in a wire cutting gate valve is disclosed in US patent no. 2010/0102263. The recess collect the wireline cutting formed after the cutting operation. However, the recess contain the cutting even after the gate moves from “closed” position to “open” position. In addition, the wireline cutting in the recess may drag against the valve block along the valve cavity, thereby possibly damaging the profile of the valve cavity. Moreover, the wire cutting gate valve disclosed above cuts tiny wireline and may not be suitable for cutting greater dimensions typically used in WCP.
Therefore, there is a need for a gate valve assembly that at least addresses the above mentioned short coming with respect to double shear valve and that may be able to handle tubing conveyed string cuttings in general, i.e. cuttings of greater dimensions than just a wireline.